As the market of portable electronic devices such as cellular phones, notebook personal computers and digital cameras expands, secondary batteries having high energy density and long life time functioning as cordless power sources for these electronic devices are eagerly demanded.
For responding to such a demand, a secondary battery having alkali metal ion such as lithium ion as a charge carrier, and utilizing the electrochemical reaction associated with donation and reception of electric charge has been developed. In particular, a lithium ion secondary battery having large energy density becomes widely used today.
Of constituents of a secondary battery, an electrode active material is a substance that directly contributes to the battery electrode reaction including charging and discharging, and plays the central role in the secondary battery. The battery electrode reaction is a reaction occurring in association with donation and reception of an electron when a voltage is applied on the electrode active material that is electrically connected with an electrode disposed in an electrolyte, and proceeds at the time of charging or discharging of the battery. Therefore, as described above, the electrode active material plays the central role in the secondary battery in terms of the system.
In the foregoing lithium ion secondary battery, which uses a lithium-containing transition metal oxide as a cathode active material and a carbon material as an anode active material, charging or discharging is achieved by utilizing the insertion and elimination of lithium ions to/from these electrode active materials.
However, the foregoing lithium ion secondary battery faces the problem that the speed of charging or discharging is limited because movement of lithium ion in the cathode is rate-limiting. In other words, the moving speed of lithium ion in the transition metal oxide in the cathode is lower than those in the electrolyte and the anode, in the aforementioned lithium ion secondary battery, so that the battery reaction speed in the cathode is rate-limiting, to limit the charging or discharging speed, and as a result, realization of high power and reduction in the charging time are limited.
A secondary battery including an organic compound as a cathode active material is proposed in recent years for solving such a problem. Research and development for secondary batteries, including an organic radical compound of such organic compounds has been actively made.
For example, Patent Document 1 proposes an active material for a secondary battery which includes a nitroxyl radical compound, an oxy radical compound, and a nitrogen radical compound having a radical on a nitrogen atom.
Patent Document 1 describes an example in which a highly-stable nitroxyl radical or the like is used as a radical, and demonstrates that when a secondary battery produced, for example, by using an electrode layer containing a nitronyl nitroxide compound as a cathode and a lithium-bonded copper foil as an anode, is repeatedly charged and discharged, the charging and discharging is possible for greater than or equal to 10 cycles.
Patent Document 2 proposes an electrode containing a compound having a diazine N,N′-dioxide structure as an electrode active material, and Patent Document 3 proposes an electrode active material containing an oligomer or polymer compound having a diazine N,N′-dioxide structure in its side chain.
In these Patent Documents 2 and 3, a diazine N,N′-dioxide compound or a polymer compound having a diazine N,N′-dioxide structure in its side chain functions as an electrode active material in the electrode, and in the discharging reaction of the electrode reaction, or in the charging and discharging reactions, it is contained in the electrode as a reaction starting substance, a product, or an intermediate product. Five different conditions can be obtained by donation and reception of an electron in the oxidation-reduction reaction, and this implies the possibility of multi-electron reaction in which greater than or equal to two electrons are involved in the reaction.